If voters agree on Nov. 4 to raise the sales tax from 7 to 8 percent, officials say the property tax that currently funds the Pinellas Suncoast Transit Authority will be eliminated.

County and PSTA officials are hammering out a pact that aims to put as much teeth into that promise as possible. It includes safeguards designed to ensure the one-cent tax money will only be used to expand bus service and build a 24-mile light rail line between St. Petersburg and Clearwater. The entire project, including the bus and rail components, is expected to cost $2.2 billion to build and $130 million annually to operate.

"The county doesn't want to micromanage it," said attorney Steve Miller, a consultant hired to represent the county in talks with PSTA. "However, if things go sideways or don't go quite as planned, the county would have the ability to insert itself."

Local officials had hoped the Legislature would give voters an extra degree of confidence that they wouldn't be taxed twice.

A bill that would have repealed PSTA's authority to levy a property tax if the Greenlight referendum passes was passed two years ago, but Gov. Rick Scott vetoed it. Scott said the issue should be addressed at the local level. Opponents of the sales tax hike feared the bill would make it easier to pass the referendum.

The agreement being forged locally would let PSTA retain its taxing authority but would allow the county to ask voters to reduce or eliminate the Greenlight sales tax if PSTA uses that power.

The agreement, which Miller calls "the key to our accountability," would also allow the county to hold back transit tax revenue or ask voters to reduce or eliminate the tax if:

• The system is built and officials determine the tax can be reduced.

• The PSTA board votes not to proceed with the plan.

• PSTA defaults on its debt or misapplies the funds.

• A catastrophic event, such as major hurricane, hits the region.

The agreement also sets major milestones taken from the Greenlight plan, such as starting the first phase of the rapid bus line by 2018 and completing light rail by 2024.

If PSTA misses a milestone, a consultant would mediate and make recommendations to get the project back on track.

"We've tried to make sure this agreement mirrors the plan and the message that is being presented to the electorate," County Attorney Jim Bennett told county commissioners during a recent update.

PSTA has agreed to adopt conservative debt and investment policies similar to the county's and would be required to reimburse the county for any impact to county infrastructure.

Another check on PSTA power is the makeup of its 15-member board. Four county commissioners hold a seat.

Commissioners are expected to review and vote on a final draft of the agreement next month.

The benefits or costs of the tax swap on individuals will vary.

The current PSTA tax is assessed at a 0.7305 millage rate. Greenlight Pinellas illustrates its plan using census averages from 2008 to 2012, taking as a case study a median family home value of $161,000. Under that scenario, the portion of property taxes that goes to the transit authority is less than $90.

Greenlight also looks at a median income family with two children earning about $46,000. Using the IRS sales tax deduction calculator, Greenlight concluded that this family will pay about $800 in sales taxes annually at the new 8 percent rate, about $104 more per year.

Under the plan, a family that owns a $161,000 home and makes about $46,000 would stop paying the $90 property tax and instead pay $104 in additional sales taxes — an increase of $14.

Opponents of the sales tax increase, including the No Tax for Tracks political committee, point out that people who don't own real estate won't benefit at all by the tax swap.

Tony Marrero can be reached at tmarrero@tampabay.com or (727) 893-8779.